Fireworks explode over the Olympic stadium on Thursday during the final rehearsal for the opening ceremony.

An expectant London prepared Friday to launch the Olympic Games with a spectacular opening ceremony in front of a crowd of 80,000 and more than one billion TV viewers.

After seven years of planning, the Games will officially begin in a gleaming new stadium in a once rundown area of east London with a show devised by "Slumdog Millionaire" director Danny Boyle.

Queen Elizabeth II will declare the Games open after a show which Boyle promised would showcase British history as well as the nation's quirky sense of humor.

More than 120 world leaders are expected to attend the ceremony, while First Lady Michelle Obama will represent the United States alongside a host of celebrities including Angelina Jolie.

The Olympic flame was rowed up the River Thames in a ceremonial barge as it approached the end of its 70-day journey, but the person who will light the Olympic cauldron remained a closely guarded secret.

The weather is expected to play its part by staying dry for the ceremony.

Once the curtain goes up, the stage is set for superstars Usain Bolt, Michael Phelps and Roger Federer to dazzle, while an army of unsung competitors are also aiming for gold.

A budget of £9.3 billion ($14.5 billion, 12 billion euros) has been spent on bringing the Games to London for an unprecedented third time, but the first time since 1948.

There have been last-minute hitches with security after 4,700 additional servicemen had to be drafted in when a private security contractor failed to supply thousands of guards.

Organizers insist it was a temporary blip in Britain's biggest peacetime security operation.

International Olympic Committee (IOC) chief Jacques Rogge declared himself satisfied with the preparations.

"I can say with pleasure that London is ready and we are eagerly waiting for the opening ceremony," Rogge said Friday.

The London organizers have stressed they are not trying to rival the no-expense-spared extravaganza of Beijing four years ago.

Instead they have promised a Games for the athletes and -- against a backdrop of global economic uncertainty -- have ensured many of the venues can be reused or recycled.

Iconic locations such as Wimbledon, Lord's cricket ground and Hyde Park will host events while the Olympic Park complex, home to swimming and athletics, has transformed the Stratford district of east London.

"It has been an extraordinary journey over seven years," said chief organizer Sebastian Coe.

Hours before the official opening, visually impaired archer Im Dong-Hyun set the first world record of the Games in Friday's ranking round and added another as South Korea broke the team record.

The 26-year-old is legally blind in his left eye with 20/200 vision, while his right eye has 20/100 vision.

The man widely expected to be the face of the Games, Jamaican track star Bolt, has endured a troubled build-up, but the fastest man in the world insisted he was ready to defend both sprint titles.

"I've had slight problems, but I'm ready to go," said Bolt, who will carry the Jamaican flag at the opening ceremony.

In the pool, Phelps, whose eight golds in Beijing took his overall medal tally to 16, needs three more to surpass the all-time record of 18.

His seven-event program gives him plenty of scope to make more Games history and anchor a US team determined to continue its dominance against Australia and a Chinese squad spearheaded by 1500m free world record-holder Sun Yang.

One of his biggest challengers is teammate Ryan Lochte, who has emerged as a serious threat in the 200m medley and 400m medley.

Australia is bringing in the big artillery with James "The Missile" Magnussen and James "The Rocket" Roberts, in the prestigious 100m freestyle.

The US have a "Missile" of their own, however, in 17-year-old Missy Franklin, who is set to become the first US woman to swim seven events at one Games.

South Africa's Oscar Pistorius, known as 'Blade Runner' for his carbon fiber prosthetic running blades, will make history as the first double amputee to compete at an Olympics.

Bradley Wiggins, fresh from his historic Tour de France triumph, and a powerful British team will fire up the home crowd in the cycling.

Federer, having won a record-equaling seventh Wimbledon title, returns to the All England Club looking to add singles gold to the doubles he won with Swiss compatriot Stanislas Wawrinka four years ago.

And the United States are clear favorites in the men's basketball with a Dream Team boasting LeBron James and Kobe Bryant.